1. Field of the Invention
The present invention relates to a technology for reducing power consumption in a storage control apparatus for storing data in at least one hard disk device and other storage media. The present invention also relates to storage systems including a storage apparatus, in particular, a storage control apparatus or a tape library control apparatus for storing data on one or more disk devices or storage media; solid state disk devices such as optical disk library control apparatuses and silicon disk control apparatuses; and a storage apparatus using a plurality of storage control apparatuses or non-volatile memories such as flash memories.
2. Description of the Related Art
In recent information business scenes such as data centers, it has been considered more important to reduce TCO (Total Cost of Ownership) in a storage system (general terms for storage control apparatuses and hard disk devices, etc.) In addition, it has been required for secured data storage for a long term. For example, banking agencies and medical institutions in Japan are obliged to accumulate their document data without deleting them by laws such as the Personal Information Protection Law.
Based on this background, a storage system should be highly reliable with a large capacity. Generally, in a storage system having a larger capacity that uses hard disk drives (hereinafter referred to as HDD), power consumption increases in proportion to increase in capacity of storage media. Specifically, owning a larger capacity storage system leads to increase in TCO including electric charges.
In the view of the above disadvantages, an effective reduction in TCO over the storages system, especially in running costs represented by a power consumption amount can be achieved by adequately storing data to an appropriate storage locations, taking various requests on stored data into account when it is required to accumulate a large amount of information, if necessary, to store the data information in a long term.
By the way, great attention has recently been focused on flash memories as a non-volatile memory. Generally, a flash memory reduces power consumption by one several tenth in comparison with HDD, providing a high speed read. A flash memory can be compact because of free from a driving mechanism that is required for HDD, and has high endurance against faults in general.
However, a flash memory has a limitation on cycles of writing due to a physical property of cells for retaining information. To counter this limitation, a so-called ware leveling adjustment has been employed, in which a control is provided to maintain correspondence between cell locations and addresses which are indicated to higher level devices and to equalize cycles of writing to each cells, resulting in enhancement in rewritable cycles for the flash memory.
Hereinafter, a flash memory is used for an element to latch information, and a flash memory including mechanism for ware-leveling adjustment and protocol processing for higher-level devices is called as a “flash memory device”. The element to latch information is called as a “flash memory”.
Although the above scheme has enhanced efficiencies in limitation on cycles of writing for a flash memory device, with respect to distribution of storage area at an element level, there has been remaining limitation on cycles of writing for the flash memory device. The flash memory has a further disadvantage in that writing speed thereof descends to the same speed as that of HDD when it is necessary to erase data before writing new data.
In order to apply the flash memory with properties as mentioned above to a storage system, a scheme for storing data on an adequate storage location has been introduced, from the view point of writing performance and reliability or costs, as various requirements for stored data in conventional schemes, as disclosed in Document 1 (see Document 1 as below).
For the sake of realizing a storage system with a lower power consumption, schemes related to MAID (Massive Array of Idle Disks) have been introduced, as disclosed in U.S. Patent App. Pub. No. 2004/0054939 and Document 2 (see Document 2 as below).
However, since the scheme disclosed in Document 1 does not allow for account differences in cycles of rewriting, writing speed and power consumption between each storage medium, there have been difficulties to provide adequate control over the storage system. In the storage systems of U.S. Patent App. Pub. No. 2004/0054939 and Document 2, destinations to which the MAID can be applied are limited, so that there have been difficulties to keep a compromise between lower power consumption and maintaining of high performance of the system. Therefore, it has been requested to realize a computer system that achieves lower power consumption as well as high performance, so as to optimize the whole storage system. In particular, it has been requested to reduce power consumption, which is a crucial issue in a data center or the like, and ensure a higher access performance as well.
Document 1: John Wilkes, Richard Golding, Carl Staelin, and Tim Sullivan, “The HP AutoRAID hierarchical storage system”, Transactions on Computer Systems (TOCS) archive, America, ACM (Association for Computing Machinery), February 1996, Volume 14, Issue 1 , ISSN:0734-2071, Pages: 108-136
Document 2: Dennis Colarelli, Dirk Grunwald, and Michael Neufeld, “The Case for Massive Arrays of Idle Disks (MAID)”, [online], Jan. 7, 2002, USENIX (U.S.A.), (Searched on Aug. 5, 2005)    <URL:http://www.usenix.org/publications/library/proceedings/fast02/wips/colarelli.pdf>
To solve the above problems, it is an object of the present invention to realize a successful balance between low power consumption and maintaining of high performance in a storage system.